In many circles it is believed that Apollo 11 never landed on the Moon. As a matter of fact, some people believe that it never left Earth. They contend that it was all a staged show, a fake and mockery. Of course, they have no proof of this belief, no evidence upon which to make their claims, but some of them will hold onto this belief until their dying breath.
These are probably the same people who stare at silverware, focusing all their mental energy on the metal objects, certain that there really is no spoon.
These are also the same people who probably think that rather than the mafia, the CIA or some shadow organization being responsible for the death of JFK, they point their nerve-attenuated fingers at McDonalds.
Roswell either didn't happen or it did- they bounce between the two with more frequency than Michael Jackson changes his skin color.
Human genetic cloning has been going on for decades, since World War II, or it's a pipe dream that will never come to be.
Nostradamus was either a fabrication of Orson Welles, an alien, a hoax or the real deal. Perhaps he's all four: an alien psychic created by Orson Welles who put hoaxes into his quatrains amidst real prophecies that Mr. Welles, like any good sci-fi writer, merely expected but couldn't count on.
As a writer myself, I only wish I could come up with a fraction of the half-baked theories these conspiracy theorists devise.